1. FIELD OF THE INVENTION:
The invention relates to a safety valve system for the completion of a horizontal section of a deviated subterranean well.
2. DESCRIPTION OF THE PRIOR ART:
In the past, those skilled in the art relating to remedial operations associated with the drilling, production and completion of subterranean oil and gas wells have relied on conventional "snubbing" or hydraulic workover units which utilize threaded or coupled remedial tubing normally inserted through production tubing for use in operations, such as perforating, acidizing and fracturing, corrosion control, pressure testing of tubular goods and vessels, cementing, clean out operations, sand bridge removal, storm valve recovery, insertion of kill strings, wireline fishing tools, and the like.
Continuous coiled remedial tubing and injectors for use therewith have contributed substantially to conventional remedial tubing operations. For example, coiled tubing, being continuous, can be inserted into the well faster than threaded and coupled tubing which is furnished in relatively short sections that must be screwed together. In addition, it is easier, when required, to pass continuous tubing through stuffing boxes and blowout preventers because its external diameter is consistently the same size and not interrupted periodically by couplings. The coiled remedial tubing normally is made of steel and is commercially available in sizes from 0.75 inch o.d. through 1.315 inch o.d., but may have a smaller or larger diameter.
Typical of such remedial coiled tubing and injectors is that generally described in U.S. Pat. No. 3,182,877. The apparatus is commercially referred to as the "Bowen Continuous Spring Tubing Injector Unit" and basically comprises a hydraulically powered injector unit which feeds a continuous remedial tubing string from a coiled or "spooled" workstring contained on a powered and generally portable reel unit into the wellhead by means of two opposed, endless, rotating traction members. Such a reel unit is generally described in U.S. Pat. No. 3,614,019. The upper end of the string which remains on the reel is conventionally connected to the hollow shaft of the reel which permits a liquid or a gas to be pumped through the coiled remedial tubing string by means of a swivel connection. The injector and reel are normally mounted on a single transportable skid, a trailer, or, alternatively, may be componently arranged on skids to facilitate convenient offshore use.
To inject remedial coiled tubing, the injector is arranged on or above the wellhead. The reel unit, containing up to approximately 15,000 feet of continuous coiled metal remedial tubing, is located preferably about 15 to 20 feet from the wellhead. The remedial coiled tubing is brought from the reel in a smooth arc loop through the injector unit and into the well through pressure retention and control equipment.
For many years the desirability of utilizing a subterranean wellbore having a non-vertical or horizontal portion traversing a production formation has been known and appreciated in the prior art. Laterally directed bores are drilled radially, usually horizontally from the primary vertical wellbore, in order to increase contact with the production formation. Most production formations have a substantial horizontal portion and, when conventional vertical wellbores are employed to tap such production formations, a large number of vertical bores must be employed. With the drilling of a wellbore having a non-vertical or horizontal portion traversing the production formation, a much greater area of the production formation may be traversed by the wellbore and the total field of drilling costs may be substantially decreased. Additionally, after a particular horizontal wellbore has produced all of the economically available hydrocarbons, the same vertical wellbore may be re-drilled to establish another horizontal portion extending in another direction and thus prolong the utility of the vertical portion of the well and increase the productivity of the well to include the total production formation.
By use of and reference to the phrase "wellbore" herein, it is intended to include both cased and uncased wells. When uncased wells are completed, the bore hole wall defines the maximum hole diameter at a given location. When cased wells are completed, the "wall" of the well will be the internal diameter of the casing conduit.
By use of the phrase "deviated well" and "deviated wellbore", it is meant to refer to wells and wellbores which comprise a vertical entry section communicating through a relatively short radius curvature portion with a non-vertical or horizontal portion communicating with the production formation. In most instances, the production formation extends for a substantial horizontal extent and the generally linear wellbore portion traverses a substantial horizontal extent of the production formation, at least up to a distance of 1000 to 2000 feet, or more. The radius portion of the wellbore has a curvature of at least 10.degree. per 100 feet of length, and preferably a curvature lying in the range of 10.degree. to 30.degree. per 100 feet of length.
In such deviated wellbores, particularly those having the longer lengths, it is difficult, if not impossible, to activate completion equipment, such as shifting tools for opening and closing sleeves, activating wash tools, and the like, by means of conventional electric or piano wireline means, which are disposed through the production tubing which, in turn, has been implaced within the well section through casing (assuming that the well is encased), or, alternatively, through open hole (if the well is not so encased).
As the well section becomes more deviated, the weight suspended from the wireline will become insufficient to actuate the tool, or, at least, to properly position it at the desired location within the deviated portion of the well. Such tools can thus be expected to become improperly lodged or unpositionable within such well. Accordingly, remedial continuous coiled tubing can be utilized to perform operations in such wells heretofore practiced by application of wireline actuated devices.
Since remedial continuous tubing must be introduced into the well through the casing and, in most instances, through production tubing, such remedial tubing, if not otherwise restricted, will serve as a conduit through which production fluids will flow to the top of the well in an uncontrolled state during a blowout of the well. Blowout preventer stacks at the top of the well serve to control the well in the annular area between the production tubing and the casing and the interior of the production tubing at all time during the completion operation. In addition, safety valves are carried on the production tubing or implaced therein by wireline to prevent uncontrolled fluid flow from the production zone to the top of the well through such conduit.
When continous coiled tubing is introduced into the production tubing, or the casing through the snubbing unit at the top of the well, it will be desirable for such tubing to carry safety valve means thereon which will permit fluid flow from the top of the well through the coiled tubing and the apparatus for remedial work in the production zone of the well, and for other known applications. However, as contemplated herein, such safety valve must also have the ability to be manipulatable between open and closed positions with integrity during the completion of the horizontal section of the well. Valves which require longitudinal or rotational manipulation of the remedial tubing cannot be utilized with complete confidence because the tubing manipulation is, of course, highly restricted in deviated wells of such configuration as contemplated herein. Additionally, hydraulically activatable safety systems using auxiliary hydraulic conduits extending exteriorly of the main control conduit cannot be tolerated in such horizontal systems.
The present invention is directed to overcoming such deficiencies by providing a method and apparatus for completing horizontal sections of subterranean wells, as described herein, by incorporation of a safety valve system in combination with remedial continuous coiled tubing which is introduceable through production tubing. In a preferred embodiment, the apparatus of the present invention incorporates a sleeve means which covers the sealing surface of the valve head which, preferably, is a flapper valve, when such valve is in the open position, to prevent contaminants and solid particulate matter in well fluids and in the remedial treating fluids, from coming into direct abrasive contact with such valve head, to reduce exposure of such valve head to corrosive and errosive materials, thus reducing the likelihood of a valve failure and thereby extending the life of the apparatus.